Novel epoxy-modified waterborne polyurethanes (EPUs) were synthesized from toluene 2,4-diisocyanate, poly(ethylene glycol) (PEG), dimethylolbutyric acid, and 2,3-epoxy-1-propanol (glycidol). The chemical structures of the EPU products were characterized by 1H-NMR and Fourier transform infrared spectroscopy. The thermal properties of the EPUs were examined by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). TGA showed that the EPUs had good thermal stability, with an initial decomposition temperature higher than 250 degrees C. DSC analysis showed that the glass-transition temperature of EPU1 was higher than that of EPU2. When the EPUs were heated above 150 degrees C, the curing reaction took place. In this study, the EPUs were used for carbon fiber sizing. The mechanical interfacial strength between the fibers and the matrix was evaluated by scanning electron microscopy (SEM) and interlaminar shear strength (ILSS) testing. The SEM images of the fracture sections of the composites proved that the interfacial adhesion between the fibers and the matrix improved after the EPU sizing treatment. The composites exhibited the highest value of ILSS after the EPU1 sizing treatment. The excellent properties of the EPUs confer it with potential applications in carbon fiber sizing. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012